Focal plane shutters for digital cameras include focal plane shutters each of which is provided with a first blade and a second blade. This type of focal plane shutter has had substantially the same structure as focal plane shutters for film-based cameras do, formerly. A first blade-driving mechanism for focal plane shutters of this type is composed of a first blade-driving unit and a first blade-driving spring, and a second blade-driving mechanism for focal plane shutters of this type is comprised of a second blade-driving unit and a second blade-driving spring. A first blade and a second blade are connected directly to the first blade-driving unit and the second blade-driving unit, respectively. In shooting, these two blade-driving units are rotated by the elastic forces of the first blade-driving and second blade-driving springs respectively, in turn. And, the first blade opens an exposure opening and then the second blade closes the exposure opening afterward, so that the light-receiving plane of an image sensor like CCD is exposed.
And, when the exposure operations of the first and second blades are complete, imaging information is transferred from the image sensor to a storage device through an information-processing circuit while the second blade is covering the exposure opening. Afterward, a cocking operation of focal plane shutter of this type is immediately performed in such a way that a cocking unit rotated from its initial position makes these two blade-driving units reverse up to their cocking positions against the elastic forces of the respective blade-driving springs. As a result, in a focal plane shutter of this type, the second blade stays away from the exposure opening in a state in which the cocking operation is complete, or a state in which the focal plane shutter of this type is on standby for shooting.
Also, mechanisms for preventing the two blade-driving units from rotating until an exposure operation is performed in next shooting include mechanisms called “locking type” and mechanisms called “direct type”. The locking-type mechanisms are formed in such a way that blade-driving units are made to engage with locking units respectively to be locked in respective their cocking positions. As a result, the cocking unit may be made to immediately return to its initial position when the cocking operation is complete, or the cocking unit may be made to return to its initial position before the exposure opening-opening operation of the first blade in releasing camera shutter. And, the respective locking units are operated by respective electromagnets and the respective blade-driving units are released from the respective engagements with the locking units in turn, so that the exposure operations of the first and second blades are performed.
On the other hand, the direct-type mechanisms are formed in such a way that: each of the two blade-driving units is provided with a iron piece element; and the cocking unit rotates these blade-driving units, until these iron piece elements come into contact with electromagnets not magnetized respectively as a result of the cocking operation. As a result, in the direct-type focal plane shutters, the cocking unit does not return to its initial position even after the iron piece elements come into contact with the electromagnets not magnetized respectively, so that the cocking unit keeps the iron piece elements coming into contact with the electromagnets not magnetized. And, when a release button of a camera is pressed in next shooting and each of the electromagnets is magnetized to attract and hold the iron piece elements, the cocking unit is made to return to its initial position. And, afterward, each of the electromagnets is demagnetized to release the respective iron piece elements from the magnetic attractions due to the electromagnets in turn, so that the exposure operations of the first and second blades are performed.
Both in the case where this type of focal plane shutter is formed as a locking-type focal plane shutter and in the case where this type of focal plane shutter is formed as a direct-type focal plane shutter, the exposure opening is closed by the first blade in a state in which this type of focal plane shutter is on standby for shooting, so that this type of focal plane shutter is in a so-called normally closed (NCL) state. Accordingly, digital cameras provided with this type of focal plane shutter are usually provided with optical view finders, respectively.
Now, there has occurred the necessity that digital cameras provided with focal plane shutter should also include electronic view finders with a crystal liquid display device or the like respectively, as well as digital cameras provided with lens shutters, in recent years. Accordingly, while the number of cameras each of which is provided with only an optical view finder as before has decreased, the number of cameras each of which is provided with both of an optical view finder and an electronic view finder or provided with only an electronic view finder has increased. And, although there is a publically-known manner in which a camera is provided with another image sensor for an electronic view finder other than an image sensor for shooting in the case where the camera is provided with the electronic view finder, it is usual to use a single image sensor both for displaying an image and for capturing an image.
However, in the case where a single image sensor is used both for displaying an image and for capturing an image, a focal plane shutter in such a case has to be formed in such a way that: not only a second blade, but also a first blade is made to stay away from an exposure opening, in the cocking state of the focal plane shutter; and, when a release button is pressed in shooting, the first blade is operated to cover the exposure opening at its initial stage, and the first blade and the second blade are made to perform their exposure operation in turn at the next stage. That is to say, the focal plane shutter has to be made to fall in a so-called normally open (NOP) state in which, while the second blade is made to operate from a state of the second blade closing the exposure opening to a state of the second blade opening the exposure opening, the first blade is not made to operate from a state of the first blade opening the exposure opening to a state of the first blade closing the exposure opening, in the cocking operation.
In order to achieve such operations of the first and second blades, a focal plane shutter is formed in such a way that: the first blade-driving mechanism is composed of two units which are a first blade-driving first unit directly connected to the first blade and a first blade-driving second unit directly biased by the first blade-driving spring; in the cocking operation, only the first blade-driving second unit is moved to its cocking position in the cocking operation of the focal plane shutter so that the first blade keeps opening the exposure opening to make it possible to observe an object with the electronic view finder; when a release button is pressed in shooting, the cocking unit is returned from its cocking position to its initial position at its initial stage, the first blade-driving first unit is rotated by the elastic force of a spring weaker than the first blade-driving spring in the process of the return of the cocking unit to its initial position (where the spring weaker than the first blade-driving spring is called “first blade-cocking spring” below), so that first blade is moved to close the exposure opening; and, at the next stage, the first blade-driving second unit makes the first blade perform its exposure operation while the first blade-driving second unit is being accompanied by the first blade-driving first unit, and then the second blade-driving unit subsequently makes the second blade perform its exposure operation. For example, Japanese Patent Application Publication TOKUKAI No. 2001-222059 (“the JP '059”) discloses such a focal plane shutter.
However, the focal plane shutter disclosed in the JP '059 is formed in such a way that, when a release button is pressed in shooting and then the cocking unit returns to its initial position at the initial stage, the first blade-driving first unit is moved just before the return of the cocking unit to its initial position is complete, so that the first blade closes the exposure opening. And, in this case, the first blade-driving first unit is rotated from a state of the first blade completely opening the exposure opening to a state of the first blade completely closing the exposure opening by the elastic force of the first blade-cocking spring, in one sitting. Accordingly, if any countermeasures are not taken, the first blade bounces large when the operation of the first blade closing the exposure opening is complete, so that the exposure operation of the first blade is not allowed to start until the bounce of the first blade stops. For example, Japanese Patent Application Publication TOKUKAI No. 2003-222928 (“the JP '928”) discloses a focal plane shutter formed in such a way that, when the cocking unit returns from its cocking position to its initial position, the first blade-driving first unit is moved at the initial stage of the operation of the coking unit returning to its initial position so that the first blade is made to start to close the exposure opening early.
However, although the JP '928 discloses a structure for making it possible to rotate the first blade-driving first unit at the stage where the cocking unit returns to its initial position when a release button is pressed in shooting, the structure for the focal plane shutter disclosed in the JP '928 is not necessarily favorable for mass-producing focal plane shutters. Now, for example, Japanese Patent Application Publication TOKUKAI No. 2007-298544 (“the JP '544”) discloses a focal plane shutter formed in such a way that: in the process of returning the cocking unit to its initial position, the first blade-driving first unit is indirectly made to follow the return operation of the cocking unit from the beginning of the process so as to make the first blade close the exposure opening; and the first blade-driving first unit is made to stop following the return operation of the cocking unit before the cocking unit completely returns to its initial position, so that the bounce of the first blade is small and the first blade favorably is stopped when the cocking unit stops in its initial position. The focal plane shutter disclosed in the JP '544 has a structure extremely favorable also for mass-production.
Now, the trend of endowing cameras with multi-function has been increasingly progressing recently, so that it is demanded that even the focal plane shutters formed as described above to make it possible to perform shooting by operating two shutter blades should be formed to make it possible to perform shooting both in the normally open method and in the normally closed method by making a selection from these method by a user before the shooting.
On the other hand, focal plane shutters used for cameras at present include a focal plane shutter in which shooting performed in the normally open method and shooting performed in the normally closed method can be switched to each other, for example, like a focal plane shutter disclosed in Japanese Patent Application Publication TOKUKAI No. 2011-113060 (“the JP '060”) and offered by the present applicant.
Now, a digital camera provided with a conventional focal plane shutter as disclosed in the JP '059, the JP '928, or the JP '544, is formed in such a way that: imaging information from an image sensor is transferred to a storage device when the second blade covers the exposure opening after the exposure operation is complete; the cocking unit is rotated after the transfer of the imaging information is complete, in order to perform the cocking operation of the focal plane shutter; and the second blade is made to perform its exposure opening-opening operation to fully open the exposure opening, for example, as shown in FIG. 11. And, the reason why the cocking operation is started after the transfer of the imaging information from the image sensor to the storage device is complete is that, if the cocking operation is started immediately after the exposure operation is complete, light entering through the exposure opening during the transfer of the imaging information meets the image sensor and the imaging information is inevitably spoiled, as known publically.
Also, even in the focal plane shutter which is disclosed in the JP '060 and in which shooting performed in the normally open method and shooting performed in the normally closed method can be switched to each other, imaging information from an image sensor is transferred to a storage means when a second blade covers an exposure opening after the exposure operation is complete, a cocking unit is rotated after the transfer of the imaging information is complete so that the cocking operation is performed, and then the second blade open the exposure opening, so that the cocking operation starts after the transfer of the imaging information from the image sensor to the storage device.
Also, this type of focal plane shutter is formed in such a way that: the cocking operation of the focal plane shutter is performed by rotating the cocking unit by a camera body-side unit; and, at this point, the cocking unit makes the first blade-driving second unit and the second blade-driving unit rotate from their exposure operation-completion positions to their cocking positions against the strong elastic forces of the first blade-driving and second blade-driving springs as described above, respectively. As a result, such a cocking operation requires time which is overwhelmingly longer than time necessary for the exposure operation.
Accordingly, in conventional focal plane shutters having this type of structure, time which it takes to acquire a standby state of the focal plane shutter for next shooting (a cocking operation-completion state) from the time the exposure operation is complete cannot be merely determined by taking only time necessary for the cocking operation into consideration, and time which it takes to acquire a standby state of the focal plane shutter for next shooting from the time the exposure operation is complete is forced to become all the more long due to the necessity to secure time necessary for the transfer of the imaging information to the storage device. Accordingly, such a structure is not necessarily favorable for the case where a user wants to perform the next shooting immediately after the completion of shooting or for the case where shooting is performed with a continuous-shooting mode.
The present invention is made in order to solve such problems. An aspect of the present invention is to offer: a focal plane shutter for cameras which makes it possible to switch shooting in the normally open method and shooting in the normally closed method to each other, which makes it possible to determine the length of time from the completion of an exposure operation to next shooting while time necessary for transferring imaging information is being hardly taken into consideration, and which makes it possible to improve continuous-shooting speed; and a digital camera provided with the same.